If it helps, I recently rebuilt my mail server and changed from FreeBSD+qmail+Courier to Ubuntu+Postfix+Dovecot. In doing so, I used this series from Ars Technica:

http://arstechnica.com/information-technology/2014/02/how-to...

It shows how to set up SPF, DKIM, TLS, anti-spam filtering, Sieve, certificate-based authentication (I still haven't figured out how to do this with an iPhone), and so on. The only bolt-on it references but doesn't explore and I actually used is the Z-Push package to implement ActiveSync.